An image forming apparatus, in which a transferring unit for transferring a toner image on a sheet is detachably mounted, has been conventionally known.
As such an image forming apparatus, there has been proposed an electrophotographic printing apparatus in which a transfer belt unit, including a loop-shaped transfer belt, a drive roller and an idle roller both wound around by the transfer belt, and a belt frame retaining shafts of these rollers, is detachably mounted.
In this electrophotographic printing apparatus, the transfer belt unit is attached or detached on the upper side of the electrophotographic printing apparatus.
In the transfer belt unit, a lock portion is provided on the belt frame, and a bearing is attached to each of both ends of the drive roller and the idle roller. On the other hand, the electrophotographic printing apparatus is provided with a lock mechanism and a bearing-receiving portion. When the transfer belt unit is mounted in the electrophotographic printing apparatus, the lock portion fits in the lock mechanism and the bearing fits in the bearing-receiving portion, and the transfer belt unit is thus positioned in an inner portion of the electrophotographic printing apparatus.
In recent years, an image forming apparatus allowing for replacement of spare parts, such as a transfer belt unit, on the user standing position side (near side), a so-called front accessible image forming apparatus, has been desired. However, the electrophotographic printing apparatus is not adopted for such front access because the transfer belt unit is attached and detached on the upper side.